LN dewar on the way. Couple questions...

S.Alexander

S.Alexander

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Jul 7, 2013
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I just purchased a liquid nitrogen dewar off of eBay and it should arrive soon. I'm pretty excited to be set up for real cryo, as dry ice is pretty expensive from my supplier up here.

I have a couple of questions though. I will have to make a lid for the dewar. Is regular styrofoam okay to use for a lid? Does the lid need a solid top or is a styrofoam plug sufficient? How do you guys transport your dewars from the supplier to your shop?

Thanks in advance.


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That's not a dewar, that is a flask. Your supplier may or may not fill that for you depending on their regulations/requirements. As far as a top, you'll need to see what your supplier requires but whatever you use, you MUST be sure that it isn't airtight.
I'm 99% sure that with something that small, all the LN will boil out when you put a blade in it. I could be wrong though. Whatever you do you better be VERY careful, LN is MUCH more dangerous than dry ice. You can lose a finger or toe in an instant.
 
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Ah you're right Darren, I had the wrong terminology. I'll have to call around and ask about having it filled. I will also purchase the proper gloves for handling LN
 
It's 14" tall with a 3" diameter. If it's not filled to the top will it still boil out? I will definitely proceed with caution.
 
Don't forget about your feet. You should always wear boots with your pants covering the tops. The last thing you want is to have a spill and wind up with a shoe soaked in LN frozen to your foot.
 
Its gonna depend on the size of the blade. You're just gonna have to experiment with the amount that works best.
 
Just to make sure you understand. A flask is for holding LN in use. A dewar is for holding it in storage. Generally, a flask has no top. It is filled from the dewar and then used. It boils off fairly quickly. It would be vey unsafe to try and transport a flask of LN more than carrying it from the dewar to the work room. I seriously doubt a supplier would fill a flask.

You still need a dewar.
 
Stacy E. Apelt - Bladesmith said:
Just to make sure you understand. A flask is for holding LN in use. A dewar is for holding it in storage. Generally, a flask has no top. It is filled from the dewar and then used. It boils off fairly quickly. It would be vey unsafe to try and transport a flask of LN more than carrying it from the dewar to the work room. I seriously doubt a supplier would fill a flask.

You still need a dewar.
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Copy that. So I have half the setup so far.
 
Also, it pay to call around for price. There are two companies that carry in my neck of the woods. The one is twice the price of the other.
 
I know a couple of local LN suppliers where I am located will fill a quality thermos if the lid has been modified to vent adequately. Might be a way for you to get LN to your shop to use your flask. In your flask with something like a vented styrofoam lid or a thermos, LN isn't going to last very long.

Your flask has a wide enough opening for most knives. Actual wide mouth dewars are more rare and often more expensive than the standard dewars with a 50mm opening. Maybe you can pick up an actual dewar to use for transport. For some knives you could also use the dewar for cryo. On blades too large for the dewar you could transfer LN in to your flask. LN will last much longer in a dewar, and typically the larger the dewar the longer it will hold LN. Before doing any transfer if LN from one vessel to another doing some reading on safe handling practices.
 
I just had a conversation about LN with my dad this morning. Boiling water is a little over 100 degrees hotter than your body. Liquid nitrogen is a little over 400 degrees colder than your body. So, relative to your skin, liquid nitrogen is much colder than boiling water is hot. But, just like quenching hot steel in water, there is a vapor jacket of boiling nitrogen that can protect you in some circumstance, but not others. I handle dry ice with my bare hands, I guess I'm just that badass, but a blade coming out of liquid nitrogen is trouble. And, like water, it does wet things. I can't imagine spilling a flask on my clothing, but I think I'd rather be on fire. There is no way I would want to handle an open mouth flask more than about half full because of sloshing. And half a flask of LN isn't gonna last very long, so I don't see this working out great unless you're pretty close to your supplier.

Perhaps you could cast it into a beer cooler with some of that polyurethane spray foam to make it more stable and manageable? For a cork, I'd use a polyethylene pool noodle before styrofoam, it's not as brittle when cold.
 
Thanks for all of the advice everyone. I will definitely do some reading on safety and will talk to my supplier about storage and transport options. Lots to think about here
 
I think Nathan's idea of stabilizing the flask in a larger container held in place with some spray foam is a good one. You could probably transport safely that way too. The LN in that flask won't last long. Might want to consider something like a thermos for getting more from your supplier at a time.
 
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